The invention relates generally to instruments for electrical measurement and more particularly to instruments for detecting the presence of AC, pulsed DC and DC voltages.
There are many situations, both industrial and in the home, when it is desirable to be able to detect the presence of an AC, pulsed DC or DC voltage. In the home, checking the 110 volt house voltage may be necessary in locating and repairing household appliances. The telephone ring circuit is powered by AC voltage as are 70 volt audio lines. The car ignition system is a pulsating DC system. An AC chopper may be utilized as a power source, e.g., in a battery operated forklift.
Thus there are a variety of potential users for an instrument to detect the presence of an AC, pulsed DC or DC voltage, from the homeowner to the engineer. The users would particularly include electricians, automotive mechanics working on automobile electrical systems, and air conditioning repairmen. The instrument will be useful for locating and diagnosing problems and lowering repair costs. In particular, an instrument for detecting the presence of voltages would promote safety. The instrument could be used to detect ungrounded fixtures and to indicate that high voltage lines were live.
It is desirable to have an instrument which provides a quick check of whether a voltage is present or not before more extensive measurements are undertaken. The most effective type of instrument would have the characteristics of small size and ease of use. The instrument would ideally not have to make physical contact with the conductor, since in many cases the conductor might not be readily accessible, or might be sheathed with insulation, or it would be safer not to directly contact an unknown source of potentially high voltage. The instrument should also be low cost to be available to the many potential users.
In general instruments are not available which meet all these requirements. Conventional voltmeters are available for measuring voltages, i.e., the potential between two points in a circuit. These are complicated instruments and require physical contact with the voltage source being measured. Other instruments are available to provide continuity checks in a circuit; however, these devices also require contact between different points in the circuit. Examples of these types of instruments are described in U.S. Pat. No. 3,704,411 to Jamieson issued Nov. 28, 1972 relating to a portable device for testing electrical appliances; U.S. Pat. No. 4,150,330 to Hudson et al issued Apr. 17, 1979 describing a fuse tester and flashlight; U.S. Pat. No. 3,227,948 to Cheshire issued Jan. 4, 1966 for a multipurpose flashlight structure; U.S. Pat. No. 3,753,090 to Tomek issued Aug. 14, 1973 relating to a combination flashlight and continuity tester; and U.S. Pat. No. 2,916,699 to Eisenberg et al issued Dec. 8, 1959 for a combination probe and continuity tester. Other apparatus is available which is large, bulky and complicated, is not portable, and requires an on/off switch to prevent rapid draining of batteries.
Accordingly, it is an object of the invention to provide an instrument for detecting the presence of AC, pulsed DC, or DC voltages.
It is also an object of the invention to provide an instrument which detects AC or pulsed DC voltages without any physical contact with the conductor.
It is another object of the invention to provide an instrument which is simple, small in size, portable, easy to use, and low cost.